Intervertebral disk prosthesis or artificial vertebra

ABSTRACT

An intervertebral disk prosthesis having an essentially hollow cylindrical base element ( 1 ) which is provided with a casing ( 2 ) that is embodied as a bellows, a top end ( 3 ), and a bottom end ( 4 ), and a central longitudinal axis ( 5 ). The base element also includes an upper apposition plate ( 6 ), which is disposed perpendicular to the longitudinal axis ( 5 ) at the top end ( 3 ) of the base element ( 1 ) and rests on the base plate of the vertebra, and a lower apposition plate ( 7 ), which is arranged perpendicular to the longitudinal axis ( 5 ) at the bottom end ( 4 ) of the base element ( 1 ) and leans on the cover plate of a vertebra. The casing ( 2 ) serves a spring element having a defined spring rate.

BACKGROUND OF THE INVENTION

The invention concerns an intervertebral disk prosthesis or anartificial vertebral body.

From U.S. Pat. No. 4,932,975 Main et al. a vertebra prosthesis is known,that comprises an expandable bellows as the basic body. The bellows ismade from a flexible material, that allows an expansion of the bellows.However, in the case of this bellows basically one deals with a passiveelement, that through an opening can be filled with a fluid, while thebellows passively stretches. Thus in the case of this known device itlacks an active elastic element that could flexibly absorb the loads. Inaddition, a further disadvantage of this known vertebral body prosthesisis that subsequently it has to be filled with a fluid, e.g. amethacrylate (in particular methyl methacrylate MMA), representingconsiderable risks.

From WO 00/35383 Dimso, an intervertebral disk prosthesis of the generictype is known. This known intervertebral disk prosthesis comprises acompressible body between two plates, said body is enveloped by abellows-like jacket. The disadvantage of this known intervertebral diskprosthesis is its low stiffness.

BRIEF SUMMARY OF THE INVENTION

This is where the invention wants to provide remedy. The object of theinvention is to produce an intervertebral disk prosthesis or anartificial vertebral body, that has axially dampening components, sothat both the translation, rotation and the angulation can be absorbedand transmitted in a defined manner.

The objective set by the invention is achieved with an intervertebraldisk prosthesis or an artificial vertebral body, having the features ofthe disclosed embodiments.

The advantages essentially achieved by the invention are that by virtueof the intervertebral disk prosthesis or the artificial vertebral bodythe function and the task of an intervertebral disk or of a naturalvertebral body can be reproduced as close as possible.

Further advantageous configurations of the invention are disclosedherein.

The comments regarding each embodiment are made in most cases based onan intervertebral disk prosthesis; all embodiments refer, however, alsoto a possible construction as an artificial vertebral body.

The specific spring rate of the spring element should be preferably atleast 50 N/mm, preferably at least 100 N/mm. The spring rate is,however, preferably 150 N/mm, preferably at least 400 N/mm. The springrate should be limited also upwards and be maximum 800 N/mm, preferablymaximum 2000 N/mm. The spring rate is typically 600 N/mm.

In the case of a load of 1000 N the spring travel of the spring elementshould be in the range of 1–2 mm, preferably in the range of 1.3–1.7 mm.The spring travel under this load is typically 1.5 mm.

According to an embodiment of the invention the spring element isconstructed both as a tension spring and as a compression spring.

The number of folds of the jacket, constructed as bellows, is preferablyin the range of 3–10, preferably 4–5. This number is advantageous bothfor the production technology and the desired stretching of the materialused.

According to an embodiment of the invention the jacket comprises aplurality of single layers. Thus the stiffness of the bellows can becontrolled arbitrarily within certain limits.

In the case of a special embodiment the single layers are spaced fromone another. By virtue of this construction various bellows can becombined with one another, that can accept various loads, e.g. anexternal bellows for the angulation, translation, rotation and dampeningof a load, for example, 800 N and an internal bellows to accept loads ofapprox. 2500 N, so that the external bellows will be protected.

In the case of another special embodiment the single layers abut againstone another without intermediate layers. Thus the stiffness can beincreased.

In the case of another embodiment the jacket comprises a plurality ofbellows inserted into one another.

The jacket may also have slots, that should extend basically parallel tothe longitudinal axis. By virtue of this the rotational stiffness of thebellows will be reduced.

The rotational stiffness of the jacket should be so chosen, that itwould allow 1°–3° rotation of the jacket, preferably 1.5°–2.5°.

When using an axial force of 800 N, the axial stroke of the jacketshould be preferably in the range of 1.0–2.5 mm, preferably in the rangeof 1.30–1.75 mm.

According to an embodiment of the invention both apposition plates arefastened on the top and bottom ends of the basic body axially firmly butenabling rotation.

In the case of an alternative embodiment both apposition plates areaxially fastened on the top and bottom ends of the basic body and theirrotation about the longitudinal axis is limited, preferably to anangular range of maximum 5°.

In the case of another alternative embodiment both apposition plates arefastened on the top and bottom ends of the basic body axially firmly andunable to rotate.

In the case of a special embodiment the rotational stiffness of thejacket constructed as bellows is so chosen, that both apposition platescan be rotated relative one another about the longitudinal axis by anangle of 1°–5°, preferably 2°–3°.

In the case of a further embodiment both apposition plates can be tiltedfrom the plane that is orthogonal to the longitudinal axis by an angleof 4°–8°, preferably 5°–7°.

In the case of a particular embodiment of the invention thehollow-cylindrical basic body is filled at least partially with a solidbody, preferably a synthetic material, acting as a dampening element. Byvirtue of this construction the stiffness will be increased and a betterabsorption of greater shock loads, e.g. 2500 N, will result.

The jacket of the intervertebral disk prosthesis can be made from ametal, e.g. titanium or a metal alloy, preferably based on titanium. Thematerial of the jacket should preferably have a minimum stretch limit of30%, preferably a minimum of 38%. The jacket can be made, however, alsofrom a synthetic material, preferably an elastomer.

In the case of a special embodiment of the invention the jacket is madefrom a packet of cup springs.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and developments are explained in detail in the followingbased on the partly schematic illustrations of several embodiments.

They show in:

FIG. 1—a perspective view of an intervertebral disk prosthesis,

FIG. 2—a top view on the intervertebral disk prosthesis according toFIG. 1,

FIG. 3—a longitudinal section along line B—B of FIG. 2,

FIG. 4—a version of the intervertebral disk prosthesis according to FIG.1, longitudinally sectioned,

FIG. 5—a perspective view on an intervertebral disk prosthesis with acentral bore,

FIG. 6—a top view on an intervertebral disk prosthesis according to FIG.5,

FIG. 7—a longitudinal section along line B—B of FIG. 6, and

FIG. 8—a perspective view of a partially sectioned intervertebral diskprosthesis with two bellows, inserted into one another.

DETAILED DESCRIPTION OF THE INVENTION

The intervertebral disk prosthesis, illustrated in FIGS. 1–3,essentially comprises a hollow-cylindrical basic body 1 with a jacket 2constructed as a bellows, a top end 3, a bottom end 4 and a centrallongitudinal axis 5. On the top end 3 of the basic body 1 a topapposition plate 6 is provided transversely to the longitudinal axis 5,that is intended as a support for the base plate of a vertebral body. Onthe bottom end 4 of the basic body 1 a bottom apposition plate 7 isprovided transversely to the longitudinal axis 5, that can be placed onthe cover plate of a vertebral body.

Both apposition plates 6, 7 have an outwardly structured surface 8, thatis made up from a plurality of pyramid-shaped teeth, so that to achievea better contact with the base and cover plates of the adjacentvertebral bodies. The structured surface 8 can be also realised in theform of etching the surface or in the form of surface structurespromoting the adherence of the bone tissue.

The jacket 2, constructed as an external bellows, has altogether threeto six folds (waves).

The height of the intervertebral disk prosthesis is 5–15 mm, dependingfrom the embodiment, the diameter is in the range of 10–35 mm and thethickness of the jacket is approx. 0.1 mm.

Both apposition plates 6, 7 have inward facing axial spigots 12 and 13,that can be constructed as dampening elements.

In the case of the version illustrated in FIG. 4 both apposition plates6,7 with the inward facing axial spigots 12 and 13 as bearing spigotsare rotatably mounted in a housing 14, while the rotation can be limitedby stops (not illustrated).

The embodiment of an intervertebral disk prosthesis, shown in FIGS. 5–7,is similarly constructed to those according to FIGS. 1–3. The differenceis that both apposition surfaces 6, 7 are constructed as annuluses, sothat a bore 9, axially passing through it, will result. A furtherdifference is that in the case of this embodiment the jacket 2,constructed as bellows, has only one fold (wave).

FIG. 8 shows particularly graphically the operation of theintervertebral disk prosthesis. In the case of this embodiment thejacket 2 comprises an external bellows 21 and an internal bellows 22.The external bellows 21 has five folds and the internal bellows 22 hasnine folds. The external bellows 21 is fastened on the top appositionplate 6 and the internal bellows 22 on the bottom apposition plate 7.Depending on the material the bellows can be welded to the appositionplates 5, 6, caulked or pressed into them. In the embodiment illustratedboth bellows 21, 22 are let into annular grooves 10 and 11, that areprovided on the inside of both apposition plates 6, 7. As FIG. 8illustrates, the two apposition plates 5, 6, that can be fastened on abellows 21, 22 each, can be fitted together to form a box. Consequentlythe two apposition plates 5, 6 can rotate relative one another. Byvirtue of a stop (not illustrated) the rotation can be limited to apredetermined value, e.g. 2°–3°.

1. An intervertebral disk prosthesis or an artificial vertebral body,comprising: A) an essentially hollow-cylindrical basic body (1) with ajacket (2) constructed as a bellows, a top end (3), a bottom end (4) anda central longitudinal axis (5), B) a top apposition plate (6), providedtransversely to the central longitudinal axis (5) on the top end (3) ofthe basic body (1), said top apposition plate (6) serving as a supportfor a base plate of a vertebral body, and C) a bottom apposition plate(7), provided transversely to the central longitudinal axis (5) on thebottom end (4) of the basic body 1, said bottom apposition plate (7)being adapted for placement on a cover plate of a vertebral body, and D)the jacket (2), constructed as a bellows, is constructed as a springelement with a specific spring rate, wherein E) the jacket (2) comprisesa plurality of bellows inserted into one another.
 2. The intervertebraldisk prosthesis or artificial vertebral body according to claim 1,wherein the specific spring rate is at least 100 N/mm.
 3. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 2, wherein the spring rate is at least 400 N/mm.
 4. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 1, wherein the spring rate is less than 2000 N/mm.
 5. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 1, wherein, under a load of 1000 N, a spring travel of the springelement is between about 1–2 mm.
 6. The intervertebral disk prosthesisor artificial vertebral body according to claim 1, wherein the springelement is both a tensile spring and a compression spring.
 7. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 1, wherein a number of folds of the jacket (2) is between about3–10.
 8. The intervertebral disk prosthesis or artificial vertebral bodyaccording to claim 7, wherein the number of folds of the jacket (2) isbetween about 4–5.
 9. The intervertebral disk prosthesis or artificialvertebral body according to claim 1, wherein the jacket (2) comprises aplurality of single layers.
 10. The intervertebral disk prosthesis orartificial vertebral body according to claim 9, wherein the singlelayers of the jacket (2) are spaced from one another.
 11. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 9, wherein the single layers of the jacket (2) abut against oneanother without intermediate layers.
 12. The intervertebral diskprosthesis or artificial vertebral body according to claim 1, whereinthe jacket has slots that extend essentially parallel to the centrallongitudinal axis (5).
 13. The intervertebral disk prosthesis orartificial vertebral body according to claim 1, wherein rotationalstiffness of the jacket (2) allows a 1°–3° rotation of the jacket. 14.The intervertebral disk prosthesis or an artificial vertebral bodyaccording to claim 1, wherein, when an axial force of 800 N is applied,an axial stroke of the jacket is between about 1.0–2.5 mm.
 15. Theintervertebral disk prosthesis or an artificial vertebral body accordingto claim 1, wherein the top and bottom apposition plates (6, 7) arefirmly axially fastened on the top and bottom ends (3, 4) of the basicbody (1), respectively, but so as to enable rotation.
 16. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 1, wherein the top and bottom apposition plates (6, 7) are axiallyfastened on the top and bottom ends (3, 4) of the basic body (1),respectively, such that rotation of the top and bottom apposition platesabout the central longitudinal axis (5) is limited to an angular rangeof no more than about 5°.
 17. The intervertebral disk prosthesis orartificial vertebral body according to claim 1, wherein the top andbottom apposition plates (6, 7) are firmly axially fastened on the topand bottom ends (3, 4) of the basic body (1), respectively, so as toprevent rotation of the top and bottom apposition plates.
 18. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 17, wherein rotational stiffness of the jacket (2) constructed asbellows is so chosen, that the top and bottom apposition plates (6, 7)can rotate relative one another about the central longitudinal axis (5)by an angle of between about 1°–5°.
 19. The intervertebral diskprosthesis or artificial vertebral body according to any claim 1,wherein the top and bottom apposition plates (6, 7) can be tilted from aplane that is orthogonal to the central longitudinal axis (5) by anangle of between about 4°–8°.
 20. The intervertebral disk prosthesis orartificial vertebral body according to claim 1, wherein thehollow-cylindrical basic body (1) is filled at least partially with asolid body that acts as a dampening element.
 21. The intervertebral diskprosthesis or artificial vertebral body according to claim 20, whereinthe solid body is formed from a synthetic material.
 22. Theintervertebral disk prosthesis or artificial vertebral body according toclaim 1, wherein the jacket (2) is made from a metal or a metal alloy.23. The intervertebral disk prosthesis or artificial vertebral bodyaccording to claim 1, wherein the jacket (2) is formed from a materialhaving a minimum stretch limit of about 30%.
 24. The intervertebral diskprosthesis or artificial vertebral body according to claim 1, whereinthe jacket (2) is made from a synthetic material.
 25. The intervertebraldisk prosthesis or artificial vertebral body according to claim 1,wherein the jacket (2) is made from a packet of cup springs.